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Revision 787252a10d9422f3058df9a4821f389e5326c440 authored by Nathan Lynch on 15 October 2021, 17:39:02 UTC, committed by Michael Ellerman on 20 October 2021, 10:38:01 UTC 
powerpc/smp: do not decrement idle task preempt count in CPU offline
 
With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we
get:

BUG: scheduling while atomic: swapper/1/0/0x00000000
no locks held by swapper/1/0.
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100
Call Trace:
 dump_stack_lvl+0xac/0x108
 __schedule_bug+0xac/0xe0
 __schedule+0xcf8/0x10d0
 schedule_idle+0x3c/0x70
 do_idle+0x2d8/0x4a0
 cpu_startup_entry+0x38/0x40
 start_secondary+0x2ec/0x3a0
 start_secondary_prolog+0x10/0x14

This is because powerpc's arch_cpu_idle_dead() decrements the idle task's
preempt count, for reasons explained in commit a7c2bb8279d2 ("powerpc:
Re-enable preemption before cpu_die()"), specifically "start_secondary()
expects a preempt_count() of 0."

However, since commit 2c669ef6979c ("powerpc/preempt: Don't touch the idle
task's preempt_count during hotplug") and commit f1a0a376ca0c ("sched/core:
Initialize the idle task with preemption disabled"), that justification no
longer holds.

The idle task isn't supposed to re-enable preemption, so remove the
vestigial preempt_enable() from the CPU offline path.

Tested with pseries and powernv in qemu, and pseries on PowerVM.

Fixes: 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug")
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211015173902.2278118-1-nathanl@linux.ibm.com
1 parent 496c5fe
Raw File
initval.h 
/* SPDX-License-Identifier: GPL-2.0-or-later */
#ifndef __SOUND_INITVAL_H
#define __SOUND_INITVAL_H

/*
 *  Init values for soundcard modules
 *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
 */

#define SNDRV_AUTO_PORT		1
#define SNDRV_AUTO_IRQ		0xffff
#define SNDRV_AUTO_DMA		0xffff
#define SNDRV_AUTO_DMA_SIZE	(0x7fffffff)

#define SNDRV_DEFAULT_IDX1	(-1)
#define SNDRV_DEFAULT_STR1	NULL
#define SNDRV_DEFAULT_ENABLE1	1
#define SNDRV_DEFAULT_PORT1	SNDRV_AUTO_PORT
#define SNDRV_DEFAULT_IRQ1	SNDRV_AUTO_IRQ
#define SNDRV_DEFAULT_DMA1	SNDRV_AUTO_DMA
#define SNDRV_DEFAULT_DMA_SIZE1	SNDRV_AUTO_DMA_SIZE
#define SNDRV_DEFAULT_PTR1	SNDRV_DEFAULT_STR1

#define SNDRV_DEFAULT_IDX	{ [0 ... (SNDRV_CARDS-1)] = -1 }
#define SNDRV_DEFAULT_STR	{ [0 ... (SNDRV_CARDS-1)] = NULL }
#define SNDRV_DEFAULT_ENABLE	{ 1, [1 ... (SNDRV_CARDS-1)] = 0 }
#define SNDRV_DEFAULT_ENABLE_PNP { [0 ... (SNDRV_CARDS-1)] = 1 }
#ifdef CONFIG_PNP
#define SNDRV_DEFAULT_ENABLE_ISAPNP SNDRV_DEFAULT_ENABLE_PNP
#else
#define SNDRV_DEFAULT_ENABLE_ISAPNP SNDRV_DEFAULT_ENABLE
#endif
#define SNDRV_DEFAULT_PORT	{ [0 ... (SNDRV_CARDS-1)] = SNDRV_AUTO_PORT }
#define SNDRV_DEFAULT_IRQ	{ [0 ... (SNDRV_CARDS-1)] = SNDRV_AUTO_IRQ }
#define SNDRV_DEFAULT_DMA	{ [0 ... (SNDRV_CARDS-1)] = SNDRV_AUTO_DMA }
#define SNDRV_DEFAULT_DMA_SIZE	{ [0 ... (SNDRV_CARDS-1)] = SNDRV_AUTO_DMA_SIZE }
#define SNDRV_DEFAULT_PTR	SNDRV_DEFAULT_STR

#ifdef SNDRV_LEGACY_FIND_FREE_IOPORT
static long snd_legacy_find_free_ioport(const long *port_table, long size)
{
	while (*port_table != -1) {
		if (request_region(*port_table, size, "ALSA test")) {
			release_region(*port_table, size);
			return *port_table;
		}
		port_table++;
	}
	return -1;
}
#endif

#ifdef SNDRV_LEGACY_FIND_FREE_IRQ
#include <linux/interrupt.h>

static irqreturn_t snd_legacy_empty_irq_handler(int irq, void *dev_id)
{
	return IRQ_HANDLED;
}

static int snd_legacy_find_free_irq(const int *irq_table)
{
	while (*irq_table != -1) {
		if (!request_irq(*irq_table, snd_legacy_empty_irq_handler,
				 IRQF_PROBE_SHARED, "ALSA Test IRQ",
				 (void *) irq_table)) {
			free_irq(*irq_table, (void *) irq_table);
			return *irq_table;
		}
		irq_table++;
	}
	return -1;
}
#endif

#ifdef SNDRV_LEGACY_FIND_FREE_DMA
static int snd_legacy_find_free_dma(const int *dma_table)
{
	while (*dma_table != -1) {
		if (!request_dma(*dma_table, "ALSA Test DMA")) {
			free_dma(*dma_table);
			return *dma_table;
		}
		dma_table++;
	}
	return -1;
}
#endif

#endif /* __SOUND_INITVAL_H */
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